This invention relates to a ceramic radial turbine rotor made of a ceramic material for use in turbochargers for automobiles and the like and gas turbine engines.
Recently, ceramic radial turbine rotors have been developed, which are made of ceramic materials such as silicon nitride (Si.sub.3 N.sub.4), silicon carbide (SiC), sialon and the like in order to utilize particular properties of the ceramic materials such as light weight, heat-resistance, wear-resistance and the like.
However, the ceramic materials are brittle, and are inferior in toughness to metals an susceptible to impulsive forces. It has been progressively recognized that a turbine rotor made of a ceramic material should be different in design from a turbine rotor made of a metal in consideration of the properties of the ceramic material. For example, with a hitherto used ceramic radial turbine rotor designed without considering the brittleness of the material, inducer portions of turbine blades actually used are often damaged by foreign substances colliding against the inducer portions. Such foreign substances consist of carbon particles produced from unburned gases and metal oxide particles included in exhaust gases and produced from exhaust gas manifolds made of a metal exposed to high temperature exhaust gases.
In order to solve this problem, it has been proposed that a metal is deposited on tip ends of blades of a ceramic rotor by using a metal spray, as disclosed in Japanese Laid-open Utility Model Application No. 61-51,404.
Moreover, it has been proposed to make tip ends of blades round or provide rounded tip ends of blades to mitigate the shocks from the foreign particles as disclosed in Japanese Laid-open Patent Application No. 59-203,808.
In the former proposal of the Japanese Laid-open Utility Model Application No. 61-51,404, it is generally difficult to deposit a metal onto a ceramic material by using a metal spray. Particularly, turbine blades are used under very severe conditions such as rapid heating to high temperatures higher than 800.degree. C., so that deposited metal films are apt to peel due to a difference in thermal expansion between the metal and the ceramic material, with the result that actual working rotors could not be obtained. Moreover, there is a tendency of the temperature at which the turbine is used to become higher every year so that metal films deposited by using a metal spray on ceramic materials are no longer used in practical applications.
In the latter proposal of the Japanese Laid-open Patent Application No. 59-203,808, the shaping the rounded tip ends of blades involves a troublesome and time-consuming operation and substantially increases the manufacturing cost of the turbine, so that the application of the proposal to industry is difficult.